TPU Characteristics (Part 1) - Guangyuan Ruifeng New Materials

Category: TPU (popular science, no product)

Release Time: 2020-06-16

Summary: Two types: polyester (heat-resistant, chemical-resistant) and polyether (low-temperature resistant, hydrolysis-resistant, mildew-proof and antibacterial); high-strength, wear-resistant, weather-resistant, environmentally friendly, non-toxic, easily recyclable and degradable, and disturbance-resistant.

Divided into two categories: polyester (heat-resistant, chemical-resistant) and polyether (low-temperature resistant, hydrolysis-resistant, mildew-proof and antibacterial); high strength, wear-resistant, weather-resistant, environmentally friendly, non-toxic, easily recyclable and degradable, and disturbance-resistant.

1. Hardness

Hardness is an indicator of a material's resistance to deformation, scratching, and abrasion. TPU hardness is usually determined using Shore A and Shore D durometers. Shore A is used for softer TPUs, and Shore D is used for harder TPUs. Hardness is mainly determined by the hard segment content in the TPU structure. The higher the hard segment content, the higher the hardness of the TPU. As hardness increases, other properties of the TPU also change, such as increased tensile modulus and tear strength, increased rigidity and compressive stress (load-bearing capacity), decreased elongation, increased density and dynamic heat generation, and increased environmental resistance. The hardness of TPU has a certain relationship with temperature. From room temperature cooling down to the transition temperature (-4~-12℃), the hardness does not change significantly; at the transition temperature, the TPU hardness suddenly increases and becomes very hard and loses elasticity, which is the result of the crystallization of the soft segment.

The relationship between hardness, tensile set, and elongation, as well as the relationship between hardness and tear strength. As the hardness of TPU increases, the 100% tensile set and 300% tensile set increase rapidly, and the elongation decreases. This is mainly due to the increase in hard segment content: a high hard segment content makes it easier for the hard segment phase to form sub-crystals or crystalline structures, increasing the number of physical crosslinks and limiting material deformation. To deform the material, the stress must be increased, thus increasing the tensile set, while the elongation decreases. The relationship between TPU hardness and tear strength is that as hardness increases, tear strength increases rapidly, and the reason is the same as the explanation for modulus.

2. Tensile Strength

In a tensile test, the maximum tensile stress experienced by the specimen until fracture is the tensile strength, and the result is expressed in MPa. Some mistakenly call it tensile strength, etc. Tensile strength is 28.3 to 62 MPa, higher for ester type and lower for ether type.

3. Elongation at Break (Elasticity, Toughness)

Elongation at break refers to the percentage of the increase in length of the effective marked portion (between the two clamps) when the film is stretched to break, relative to the initial length of the effective marked portion (between the two clamps). Elongation at break is a measure of toughness (elasticity). A larger elongation at break indicates that the material has a certain elongation when resisting impact and will not immediately fracture.

4. Tear Strength

When an elastomer is used, it is destroyed due to the expansion of cracks, and tear strength is the evaluation of the material's ability to resist tearing. For general film materials, the longitudinal and transverse properties are often different, so samples should be prepared and measured separately.

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